The $100 million trial is the cornerstone of the Alzheimer's Prevention Initiative, a new international collaborative effort to accelerate the evaluation of promising but unproven therapies for the prevention of AD.

The double-blind trial will evaluate crenezumab, an investigational anti-amyloid antibody, in approximately 300 people from a large extended family in Colombia who share a rare genetic mutation that typically triggers AD symptom onset at approximately age 45 years. The drug will also be evaluated in a smaller number of individuals in the United States. All participants will be aged 30 years or older with normal cognitive function at enrollment.

To avoid revealing the genetic status of the participants, most of whom do not want to know if they have the genetic mutation that increases their AD risk, the study will also include relatives who are noncarriers who will receive placebo.

The participants will receive injections of crenezumab or placebo at fixed intervals for up to five years. Researchers will use imaging techniques, cerebrospinal fluid tests and cognitive measures to monitor whether accumulation of amyloid and certain other proteins in the brain is reduced, whether brain size and function is maintained and whether mental performance is preserved.

The study will test the "amyloid hypothesis," which suggests that accumulation of the amyloid protein in the brain plays a key role in the progression of AD. Preclinical data indicate that crenezumab works by binding amyloid proteins and clearing them from the brain.

Genentech will contribute the majority of the funding for the trial, in addition to providing the study drug, as well as clinical and operational expertise.

Crenezumab is also currently being evaluated in a Phase II trial of patients with mild to moderate AD symptoms. The drug was selected for use in the prevention trial with guidance from an expert advisory panel.

Genentech is developing crenezumab in collaboration with Swiss biotech company AC Immune SA.